1. Field of the Invention
In general, the present invention relates to concrete compositions that contain reinforcement fibers. More particularly, the present invention relates to concrete compositions containing fibers that chemically bond to one or more elements within the concrete composition.
2. Prior Art Description
There are many types of reinforcement fibers that have been added to concrete mixtures. The purpose of adding fibers to concrete is usually to improve the tensile strength, ductility, abrasion resistance, and/or impact resistance of the object being formed from the concrete. The use of reinforcement fibers can also provide concrete objects with some control over plastic and thermal cracking as well as post-crack strength.
Traditional fibers used to reinforce concrete mixtures include polypropylene fibers, polyolefin fibers, steel fibers and/or fiberglass fibers. Prior art that uses such traditional reinforcement fibers is exemplified by U.S. Pat. No. 4,093,471 to Greig, which discloses fiberglass reinforced cement composite materials; and U.S. Pat. No. 7,419,543 to Destree which discloses metal fibers used in a concrete mixture.
Reinforcement fibers are often used with high strength concrete mixes. Traditionally, high strength concrete mixes are those that exceed a 28-day compressive strength of between 5,000 psi (34 MPa) to 20,000 psi (136 MPa). Preferably, such high strength concrete mixes exceed a 7-day strength of 5,000 psi (34 MPa). Currently, high strength concrete mixes that incorporate reinforcing fibers for added ductility tend to lose considerable strength and toughness because of the presence of the fibers. Furthermore, the addition of the reinforcement fibers often adversely affects other important attributes, such as resistance to abrasion and resistance to cracking, particularly during freeze-thaw cycles.
When prior art reinforcement fibers, such as polypropylene, Nylon, fiberglass or steel are mixed with concrete, the reinforcement fibers merely become encapsulated in the cured concrete. The reinforcement fibers are chemically separate and distinct from the composition of the concrete. The fibers do not chemically react with the concrete mixture or otherwise chemically bond to any of the compounds found in the concrete mixture. Thus, as the cured concrete is repeatedly cycled with heat and stress, the reinforcement fibers can loosen within the concrete. Once loosened, the fiber serves no purpose other than to provide a stress concentration point in the concrete where a stress crack can develop.
Further, since traditional reinforcement fibers do not chemically bond with the concrete mixture, the reinforcement fibers create defects in the composition of the concrete. The number of defects is proportional to the amount of reinforcement fibers being used. If too many reinforcement fibers are used, the weakness in the concrete caused by the presence of the fibers can surpass the strength benefit added by the presence of the fibers. Thus, concrete products can easily be made weaker by the use of reinforcement fibers if too many are used or if the fibers are not uniformly dispersed within the concrete.
Annually, thousands of tons of fiber reinforced concrete products are reclaimed, recycled, milled or removed from service and disposed of as waste products due to failure. The failure mechanism affecting the concrete product is typically due to age, overweight loads, environmental freeze-thaw failure, abrasion, grinding, wear failure, impact or even accident. Concrete products that fail are usually expensive to remove, recycle and replace. If the concrete products were made tougher and stronger in the first place, there would be less expense required to maintain concrete infrastructure.
A need therefore exists for a system of reinforcing concrete mixtures with fibers, wherein the benefits of the added fibers are maximized and the adverse affects of the added fibers are minimized. A need also exists for a system of reinforcing concrete mixtures with fibers, wherein the fibers chemically bond to the concrete mixture, rather than being merely encapsulated by the concrete mixture. In this manner, the presence of fibers do not create defect voids in the physical structure of the concrete.
These needs are met by the present invention as described and claimed below.